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This article is still being revised. It has been tentatively accepted for the ACM Computing Surveys hypertext issue.

Xanalogical Media: Needed Now More Than Ever


"The Web versus Xanadu" THE PARADIGM CHALLENGE

Paradigms always acquire the magical patina of apparent certainty.  The views and methods of any current paradigm seem to be the architecture of the universe, rather than someone's arbitrary choice; alternatives are impossible for many people to imagine.  (As a rule, paradigms can only be perceived in contrast to other paradigms.)  But there are no simple arguments for one paradigm against another.  The differences are global, diffuse and panoramic.

The Xanadu paradigm is very different, simple but difficult to present.  The structure proposed by the Xanadu project (7, 1, 2, 5, 8, and expounded here in later sections) has always been a simple concept, but remains for most people an unimaginable paradigm challenge.*

*David Durand has says of the defining document, *Literary Machines* (9): "I never found anyone else who read it as a design specification and problem statement, even among those who've read it."
1.  The XANADU PARADIGM IN GENERAL-- Versus Files, Hierarchy and Today's Windowing Systems

The Xanadu ideal is to model and enact exactly a new world that users would want and need if they realized it was possible.  The most general statement of the Xanadu paradigm is this: the purpose of computers is tracking connections.  A new computer world must be created built around explicit connection.  Great efforts must be made toward this end.

The present computer world is built on crude traditional models: hierarchy (believed by some to be synonymous with "structure"); paper analogies, machine analogies, spatial analogies; a crude model of time and backtracking.   Older computer methods have great unseen drawbacks, pushing huge problems out into users' laps.

Users' needs are ill-addressed by the paradigm of hierarchical files and their inability to deal with non-overlap.  Today's graphical front ends, all using the arbitrarily conventionalized PARC User Interface (PUI-- usually called 'GUI') merely sugar-coats this hierarchical structure.  And paper simulation, as in "word processing", is a dumb-down bargain with the devil.  The assumption of printout as a canonical form of information (the role of the Xerox Corporation here was no accident) are clumsy constructs, entrapping the user in their irrelevant ramifications.  The same goes for "Folders", the so-called "Desktop" and worst, the pernicious "Clipboard".  Machine analogies and spatial analogies are just as misleading.

We need instead a rational representation of structure-- from computer mechanisms to electronic literature-- around the representation of all connection, rather than on false approximations (eg copying).  This includes a different approach to files (making their contents more streamlike).  Most important, it means system-maintained connections in vast quantities.

The objectives are: the escape from paper, finding the best ways to support human thought and creativity-- building on a sophisticated knowledge of complex documents, not building up from the simplest implementation of the simplest documents.  The search is for an orderly, fast-evolving, fast-accumulating universe of electronic documents, not modelled to paper, and showing detailed relations among documents and versions, including overlap and commonality.


Hypertext is a predestined form of media.  Just as writing was implicit in speech, hypertext is implicit in writing.  Hypertext and hypermedia are the manifest destiny of media (data objects with creators and points of view) and literature (media we keep).

A literature is an the media that get saved (including films, audio, etc.)-- an overall system of documents, publications, their ownership and persistence.  Today's paper literature is complex and highly evolved.  Such concepts as "document" and "version" are literary concepts.  Document and version boundaries are implicit in the sytem of literature.  Authorship and ownership of content are also part of the literary system.  Quotation, which brings in materal across a document boundary, is a literary construct.

Today we face the challenge of designing a new literature.  The issue is how to design a literary system for both change and continity, with the ability to present such literary concepts as alternative structures, disagreements, forms of evidence, correspondences, annotation and side-by-side intercomparison.  (Thus parallel hypertext is crucial.)

These are the basic concepts of the Xanadu paradigm.  They have led to a number of emergent objectives-- design aspects of the intended system that will live up to these ideas.


From the begining, we designed in the Xanadu design for one fundamental visualization.  This visualization would allow annotation (in a parallel window), intercomparison (in a parallel window), link following (in a parallel window), and many other functions.

Working backward from this visualization, all information structures had to be set up for sideways interconnection and presentation.  That is what the Xanadu project has been about.

The basic visualization is very simple.  The following pictures of it were published in 1972 (9).  They propose, and illustrate, a generalized method for showing connections and correspondences on a computer screen.


The 1972 mockup: connections between contents of windows

The first picture shows a user sitting at a mockup of a windowing system where content within one window actually connects to content within another window.   I have recently proposed the term *transpointing windows* for this interface (8), but clearly it is not just an interface, since mechanisms are required to implement this structure.  I believe such an interface and structure offer far higher capability than the windowing systems we have today (which I believe were designed later).

Closeup of the 1972 mockup.  The idea is that
the transpointing lines remain connected to content
even as the content scrolls or the windows move.

Why have such windowing systems for intercomparison not become available?  I believe they are needed everywhere, in virtually every activity.  I think the answer is twofold: those who knew it was possible saw no point (since they knew enough to get a lot of payoff for doing much less); and those who appreciated the need-- if there were any who appreciated it-- did not imagine it to be possible.

If we are to have a serious pluralistic hypertext literature, it is necessary that anyone be able to make links to anything, and this means that the links must be able to overlap.  This means that hundreds (or hundreds of thousands) of user-authors must be able to make links to the same or overlapping portions of the same material.

The link-anchor is thus a pernicious idea, based on the notion of small numbers of links to eligible locations which must be individually prepared.


The Central Transclusion Concept

We need to able to recognize shared material, and see it side by side.  Such a capacity must be supported at the system level, for managing and intercomparing identities between documents and versions.

*While the word "transclusion" has caught on here and there,
it has been widely misunderstood, and confused with
the computer mechanism of call-by-reference.
  For this reason I have more recently proposed the term
for the intercomparable presentation of identical contents (22).
Transclusion must be system-supported, not added at the application level.  Such a facility, at the system level, is vital for many study and organization purposes.  This is transclusion.*

Actually transclusion is a *literary* concept.  Literature is the system of what gets saved, esp. documents, publications, their ownership and persistence.  And such concepts as document and version and their boundaries are literary concepts.  Therefore transclusion-- recognizing and seeing contents across such boundaries-- is a literary concept.


Transclusion is an answer to the problem of understanding identities of contents-- seeing what things are the same in two documents, side by side (as in the above visualization of transpointing windows).

Because this idea is not widely recognized as important, let us consider its origins from several directions.

OFFICE ORIGIN OF THE TRANSCLUSION IDEA.  There are numerous paper methods that refer to some original: making copies; cross-indexing (with notes that say "see elsewhere"); cross-filing (putting several copies of the same document in different places where it might be sought).  ALL THESE ARE CRUDE APPROXIMATIONS OF SOMEHOW PUTTING THE SAME THING IN ALL THE RELEVANT PLACES, SIMULTANEOUSLY CROSS-VISIBLE.  All these approximations require correcting a bunch of copies every time an original changes.

COMPUTER ORIGIN OF THE TRANSCLUSION IDEA.  All digital copies implicitly refer to an original.  Why cannot the connection to the original be maintained?  Multiple copies, or other approximations to the correct relation, is a crude simulation

But making this connection to the original explicit, and maintaining such connections at the system level, requires different and expensive steps and a major commitment.

The steps required are expensive and require a major commitment.  But this proposal represents a tenable design philosophy.  But it requires extremely radical changes in the way everything is done.

LITERARY ORIGIN OF THE TRANSCLUSION IDEA.  In so many things we read, study and research, we must track the origins of content.

• Transclusion for versioning: Authors need to keep track of versions, and where some part of a version came from (often a previous version).

• Transclusion for the safety of our writings. Today's computer systems are perilous for authors, because there are so many possible ways to lose work.  But if everything an author typed in was appended to one long file, and the other documents transcluded material from that file, it would be much safer for the author's work-- NOT LOSING CONTENT, appending all inputs immediately and referring to them thereafter.

• Transclusion for overlays.  There is currently no way to create overlays on the Web, and if there were, such a facility it would probably be necessary to use some of the content in order to highlight it.

• Transclusion for drill-down access to original materials. We read reviews of many books and films we can never have time to read or see.  The reviews are tantalizing because they offer quotations which we cannot follow.  But what if excerpts were available from the review?  What if we could jump at once from an excerpted shot to the film itself?  It would be a vast improvement if a review could give direct access to the corresponding part of the actual work.  These are examples of transclusion.

• Transclusion for explanations. In order to create a document which explains another document, and uses part of its material, it is necessary to be able to legitimately obtain parts of the content.  It should be possible to annotate and excerpt materials to explain them better.

• Transclusion for Rights Management.  If each quotation could be bought by the downloading user from the original author, it would greatly simplify handling on-line copyright.  This is the Xanadu model of sale.

All these need the transclusion concept: a way to create new documents which use portions of existing documents, or parallel documents which deeply re-use the material.  If transclusion (or visible identity, or hyper-sharing) is available at the sytem level, we are all richer.
It is possible to implement this.


The standard explanation of Xanadu systems (2) has generally distinguished between two orthogonal forms of connection: links (connections between things which are different) and transclusions (inclusion from across a document or version boundary; or connection between things which are the same).  Link and transclusion must use different mechanisms: to implement transclusion by the same pointer mechanism as links prevents their use in a complementary fashion, for example with the same links to all instances of a transclusion.


Delivering and Selling material across document boundaries, or "tramspublishing"-- our copyright concept-- is likewise a literary issue (21, 23).

The traditional contrast is between defended copyright (requiring relatively complex negotiation and prepayment for use) and public domain (material which may be freely quoted and XXx.

The idea is to create a new middle realm, one which renders copyright benign and flexible.  This method will extend the benefits of quotation and anthologizing without negotiation to copyrighted material.  As construed, we consider it to be benign, fair, honest and cheap.  It is a win-win system, as it is beneficial both to rightsholders and to users, in a way that other copyright systems are not beneficial to users.

The method is basically simple: deliver each quoted portion from the original (or a cache) controlled by its publisher.  If payment is involved, payment is proportional to each publisher from each user who downloads material from that publisher.

There are several advantages.  It uniquely offers everyone the ability to re-use and recomposite materials from many sources without negotiation, making many materials easily includable, facilitating ease of recomposition as if the material were in the public domain.  And it provides direct access to the original context of every quotation.


The literary constructs of the Xanadu system are simple: parallel hypertext (showable, for instance, in transpointing windows), and showing links and transclusions (showing, for instance, as bands stretching between parallel documents and versions).

Over the last four decades, we have had a number of designs for doing these things.

For explanatory value, let me discuss first the internal design of 1972, which was the design underway when those earlier pictures were made.

The 1972 Internals

In order to show a link on the screen as illustrated in the transpointing windows above, each document must be kept aware of the link, and somehow both ends of it.  This makes it possible to project the relevant points in each document through to the screen and the user interaction layer.

This was essentially the Xanadu design of 1972: connections are defined between document positions in pairs of individual documents.  (Transclusion was omitted from that design.)

1972 Xanadu design (simplified):
link pointers reciprocated between documents
Unfortunately, keeping track of such specific connections within pairs of documents is hopeless in the general case.  If the mutual connections between two documents must be recorded in each, the combinatorial explosion becomes disastrous as the number of connected documents grows.  And this certainly does not begin to handle the problem of maintaining links as versions succeed each other.

The greater question-- how to do this for many windows, and for many documents, having such connections-- opens up the issue.  That is what we have worked on since.

The Gregory-Miller Generalization

This design was radically changed and perfected in about 1980 by Roger Gregory and Mark Miller of the Xanadu Project, as described in *Literary Machines* (2).  They generalized it for linking among many documents and to allow the sharing of materials among documents and versions.  This became the basis of the Xanadu 88.1 implementation (2).

This method assigns all media elements to a grand address space.  The universal address space includes not just addresses for the documents themselves, but assigns addresses to the actual *contents* of documents and versions, *rather than to particular positions in them*.  This gives a unique universal address to all media elements, such as text bytes or video frames.

The link is no longer between particular documents.  Now the link can be made between the actual contents of one document and the actual contents of another.  In this more general design, the link refers to these elements by their grand addresses, and ignores the internals of individual versions.

Generalized address space attaches link to contents,
which therefore may be seen in all versions.
(The link itself also has an address in the general address space.)

This then solves (in principle) the issue of how to maintain links among versions.  It means that contents may be poured and moved between versions without dislocating links.  The stabilized address structure means that any re-use of the same contents will have the same links, in whatever documents or versions they are used.  From any version it is possible to find the same links on another version, provided that any of the elements remain.

(However, the mechanical steps of following a link have an entirely different structure (2), also discussed below.)


This leads to a full definition of Xanalogical structure, as generalized from the Gregory-Miller model.  (Note that models with these levels were in our designs starting in 1960, but the Gregory-Miller model resolved a number of difficulties with it.)*

* Those who are interested in Xanadu archaeology will be interested
in small variants of these designs, but these need not concern us here.
The interior structure below this conceptual design has several levels.

Virtual streams or scrolls of registered media, append-only-- text, audio samples, video frames.

Simple constructs (lists and sequential prose) are constructed virtually out of reference pointers to this material.

Secondary constructs and interaction applied to these.

Links and transclusions have been represented by different means in different designs.  Since 1981, with the Gregory-Miller generalization, content links have been defined on ranges of lower-level elements.  Transclusions are not specifically represented, but recognized by this system as identical ranges of the address space.

THE THREE-LEVEL MODEL* • [first presented 1968] •
• Note that all these are at the conceptual level, MAY BE VARIOUSLY IMPLEMENTED •*variations to be discussed

By conflating all these levels into one closed structure, the embedded markup languages paralyze and constrict what can be done.


where content of the virtual documents is presented and manipulated
Metastructure: further levels of construction
Content pointer lists:
REFERENCE LEVEL: Virtual Documents and Virtual Versions
pointers at the scroll level of data provide for the rearrangement of content
VIRTUAL STREAMS, their identity and addressing

of stabilized data


This changes the nature of a document's digital representation. Documents defined in such a space must be represented and edited differently.

The canonical form of a document or version now must be a list of content elements.  (The document may be delivered in other forms, but regardless of how it is delivered, the referential form defines it-- as a structured list of pieces.)

Note that the general operative concept may now be called the *version* instead of the "document", since there is no implementation difference between a version and a document, only the difference in the metastructures of naming and ownership; and "version" becomes the more general term.

Because a document or version is now a structured list of contents in a generalized address space, editing needs always to maintain reference to this address space.  While the characters of text will necesssarily be present in the editing program, the editing program must also keep track of their universal addresses, and the result of editing must be the referential form, a structured list of pieces.

There is a psychological barrier to the acceptance of this method.  It is hard to explain why it is needed, especially to those in the "text is a simple application" school of thought.  Because characters are easy to copy, it seems an unnecessary level of indirection to maintain the universal address of each character as well as its representation.

However, there is one area where referential editing is well established and accepted: video and film.  For years in the video industry, the product of a final edit has been the list of video shots in a final version (Edit Decision List, or EDL), together with effects intended to take place on them.  This is now also the case in films, through the influence of such non-linear editing systems as the Avid.

However, to use this method for editing text rather than just video, we will also need text editing systems which similarly maintain such a referential form, in which contents are not merely moved around (as in most word processors), but retain also their original identity in the generalized address space.  The editing system must recognize the identity of all text contents in the general address space, and maintain their identities as the document evolves.  An example of such an editor is OSMIC, which may be found at http://www.xanadu.com.au/ted/OSMIC/OSMICpage.html.

(There is a key difference between text and video in this regard: in the case of video and film, the contents are static, meaning that the person editing does not create new shots as needed, but rather makes do with the shots on hand.  In the case of text, however, an author may continually add contents while making other editorial changes.  This means that new text must be continually assigned universal addresses as it is being created.  This is the case with OSMIC.)


Putting the links on content creates a clean design.

But the issue is, of course, the problem of a vast number of overlapping links.  Since in principle any number of links may attach to a given range of characters in a document, the process of following a link is far more complex than with (say) HTML.  Given a specific stretch of elements, the problem is checking what endsets overlap the selected stretch, establish what links attach to that stretch, and negotiating, from among that potentially huge number of links, those which are of interest and following them.

In other words, it is a complex selection problem on a potential database.  This is what is addressed by "XOC Green".


From 1960 to 1979 I operated mostly alone.  In 1979 a stable group united around the project.  Nine years later in 1988, the project was acquired by Autodesk.  After four years we experienced sudden decompression when Autodesk dropped the project.

We have not been much in touch with the rest of the world because our views of what was important, and the right methods, was totally different from anyone else's.  However, some seem to think that our software concepts were invalid because we did not deliver product.  This is absurd.  The project suffered from the "too many cooks" syndrome at both design and administrative level.  (Everyone believed the project was important, and there was a good deal of jockeying to influence or control it.)  Incidentally, my own role was reduced to spokesman and eventually fall guy, by the so-called "Silver Agreement", which barred me from a role in design or administration.

In any case, the whole system was designed backward from the aforementioned concepts of parallel hypertext-- parallel intercomparison and annotation with bidirectional links and transclusion; and from the idea of transclusive publishing, where the unit of sale of content would not be the book or magazine but the sentence or paragraph, micropurchased in arbitrary constructions which anyone could create.  We anticipated a unified, CompuServe-like, service that would provide storage and publication services, and manage fractional royalty payment for every download on an exact and fair basis that would facilitate unrestricted virtual republishing.

These ideas are still valid, and are now being redesigned in pieces for the Net.

XOC, Inc. retained the rights to the software as developed under Autodesk, and has now officially decided to make this code available under Open Source.  The designated node for finding the material will be open.xanadu.com.

Rethinking the Xanadu Project for Today's Environment

These structures are just as good as they ever were.  This is still a valid and powerful paradigm, a deep-seated and principled alternative to hypermedia-- and indeed the computer world-- as we know them today.

Since the 1992 decompression and the 1994 explosion of theWeb, I have been thinking over how these ideas may be transposed to today's Internet environment.  This meant separating out a number of constituent ideas.

The fundamental design-- referential documents and versions selecting content from stable, addressablemedia which bear the links--seems to me as good as gold.  The problem is how to XXXX for the present environment.

The different implementation structures below handle different aspects bringing of the design to the distributed model of today's Internet.

The idea is simple, but diabolically tricky to explain.  This was true of the other YYYY, now of ZZZ the idea The same applies to the components of the distributed system.  The YYYYY piecemeal to today's Internet, but to enumerate the pieces makes them sound complex and disconnected, which they are not.  Overriding concepts include:
*Transcopyright* (21).  Transcopyright is the enabling legal doctrine, endorsed by lawyers, to enable unfettered virtual transpublishing without negotiation.

*Transpublishing* (23,24).  Transpublishing is the delivery of quotations from own publisher (or some virtual equivalent).  This requires transquotation servers (21, 23) which will deliver small selections on request.

A number of specific services by Internet Service Providers (ISPs), not yet available--
long-term guaranteed publishing (this is not a technical issue, but a business promise, comparable to insurance);

address servers allowing content itself-- not merely closed titles-- to have a plurality of address locations, not merely closed titles;

micropayment which may be interposed before delivery.

Other components are needed in the user's system, particularly caches and editors which know the generalized ID of contents.

And finally, and most important-- a comparison browser based on transpointing windows.  At the University of Southampton, Ian Heath and I have created an interesting implementation which manages such connections and their scrolling. (24).  We have a working demo which enacts fully the functions of the 1972 mockup pictures.

As these windows are scrolled or moved around the screen, the lines adhere to the content, as in the original specification published in 1972.

(Note that this was programmed according to what we refer to above as the the 1972 method.)

Even computer sophisticates express surprise that this is possible.

Influences of the System
Claims that "Xanadu was a complete failure" are absurd.  While we have not yet delivered any product based on these designs, the influence of the Xanadu project has been considerable.  For instance, to mention only acknowledged instances:

• Tim Berners-Lee cited our ideas in his original proposal for the Web [URL]
• Lotus Notes came out of a discussion between Ray Ozzie and the author (14);
• Microcosm, inspired by the Xanadu work, uses external parallel links with great success (10, 11, 12);
• HyperWave uses transclusion at a large-grain level, as inspired by our work (15);
• Sam Epstein's Imedia system uses transclusion as a unifying concept for a networking version of Lambda Moo (16);
• Miller & Ping's "Crit" (18) has a Web-specific form of commentary visible through proxies.

Possible Effects on the Computer Field Itself
The emerging role of the computer as a media machine is clear, but its consequences are not generally recognized.  One is that media contents will be ever-arriving and ever-growing.  Users will accumulate digital material in vast quantities, much of which will be re-usable in new contexts.  This means is that content will need persistent identities based ever-changing projects as well as copyright ownership, and that computers will need to be set up for the rapid and routine acquisition of vast amounts of content.  Being able to make links to this content, wherever used, will be vital.

At a deeper level, there is a great deal of traditional structure in computer files and programs, whose clumsiness is seldom acknowledged; which might well benefit from fine-grained linkage and transclusion as system facilities.

There seem to be many levels of emotionalism and personal identity involved with the issues discussed here.  They certainly are not merely technical.  The Xanadu idea has challenged many people's notions of closure, connectedness, completeness, hierarchy, and proper style of work, publication and ownership.

Those who see subjects as bounded and hierarchically related, who see research as final, who see education as memorization and skills, who believe there are authorities who really understand things, who don't worry about lost information, who don't worry about minority points of view, who don't see the need to express alternatives, who don't see a need for intercomparison, who don't see a need for literary continuity, and who believe that work must always be finished and closed, have a great deal of difficulty with this paradigm.

However, for some of us who want to increase the power and accessibility of media in the future, it is hard to imagine an alternative.  This is still a valid and powerful paradigm, a deep-seated and principled alternative to the hypermedia-- and indeed the computer world-- as we know them today.

Numbered according to current text --

(1) Theodor H. Nelson, "Replacing the Printed Word."  (S.H. Lavington, ed., Information processing 80 (Proc. IFIP 80 World Computer Conference), North-Holland Publishing Co., 1980, 1013-1023).

(2) Theodor H. Nelson, *Literary Machines*, 1981.  Most recent edition, 1993 (*Literary Machines* 93.1.)  Translated also into Japanese and Italian.

(3) Richard P. Gabriel, "Lisp: Good News, Bad News, How to Win Big" at
 especially section entitled 'The Rise of ``Worse is Better'''

(4) Theodor H. Nelson, ”Embedded Markup Considered Harmful.”  In XML:  Principles, Tools, and Techniques (World Wide  Web Journal 2:4, fall 1997).  Table of contents at http://www.w3j.com/xml/

(5) Theodor H. Nelson, 1987 Xanadu Poster [to be scanned and on line shortly]

(6)  David G. Durand, personal communication.

(7) Theodor H. Nelson, "A File Structure for the Complex, the Changing and the indeterminate."  Proceedings of the ACM National Conference, 1965.

(8) Theodor H. Nelson, ”The Heart of Connection: Hypermedia Unified by Transclusion.”  CACM August 1995, vol 38 no 8, pp. 31-33.

(9) Theodor H. Nelson, “As We Will Think."  Proceedings of Online 72 Conference, Brunel University, Uxbridge, England, 1972.

(10)  Davis, H.C. "To Embed or not to Embed", CACM, 38 (8), pp108-109, August 1995.
(11) Wendy Hall, personal communication.
(12) Hugh Davis, personal communication.

(13)  Ian Feldman, "What Is Setext", at http://www.bsdi.com/setext/setext_concepts_Aug92.etx

(14)  Ray Ozzie, personal communication.

(15)  Hermann Maurer, personal communication.

(16)  Samuel Latt Epstein, personal communication.

(18)  Available at http://crit.org.

(19)  Richard M. Stallman, personal communication.

(20) Theodor H. Nelson, "Transcopyright: Dealing with the Dilemma of Digital Copyright."  Educom Review 32:1 (January/February 1997), 32-5.

(21) Theodor H. Nelson, "Transcopyright: A simple legal arrangement for sharing, re-use and republication of copyrighted material on the Net."  Keynote at WWCA '97 conference, March, 1997, Tsukuba, Japan; published in Takashi Masuda, Yoshifumi Masunaga and Michiharu Tsukamoto (Eds.), Worldwide Computing and Its Applications (proceedings of the WWCA '97 conference, Tsukuba, Japan, March 10-11, 1997.)  Springer-Verlag, Berlin, 1997.  ISBN 3-540-63343-X.  Pp. 7-14.

(22) Theodor H. Nelson, *The Future of Information*, 1997.  Available on the Web at http://www.xanadu.com.au/ted/INFUTscans/INFUTscans.html.

(23) Theodor H. Nelson, "Transpublishing: A Simple Concept", at http://www.xanadu.com.au/ted/TPUB/TPUBsum.html

(24) Theodor H. Nelson, "Transpublishing for Today's Web: Our Overall Design and Why It Is Simple".  At http://www.xanadu.com.au/ted/TPUB/TQdesign99.html

(25) Theodor H. Nelson and Ian Heath, "Implementation of Transpointing Windows."  In preparation.

(99) Theodor H. Nelson, "The Tyranny of the File."  Datamation, 15 December 1986.